Page 51 - Pharmaceutical Analytical Chemistry II - Pharm D- 02-06-07102

Hg2Cl2 (s) + 2e− ↔ 2Hg + 2Cl− (aq) calomel electrode

ESCE = E0 − 0.059 log [Cl−]2
2

Saturated

"SCE"

HgHg2Cl2(sat’d) , KCl (sat)
Its potential at 250C is 0.244 V

Silver/silver chloride reference electrode

It consists of:
- Ag wire coated with AgCl
- Solution of KCl sat'd with AgCl

Ag/AgCl (sat’d), KCl(sat’d)║
The electrode potential is determined by:
AgCl (s) + e− ↔ Ag + Cl− (aq)
EAg/AgCl = E0 − 0.059 log [Cl−]
The potential of saturated Silver/silver chloride electrode is 0.199
V at 250C ---- E0 = 0.222 V

50